Television receiver cathode ray tube displays have become commonplace in the television industry and indeed represent the normal television display system. While the designs of cathode ray tube displays are subject to great variation, all generally utilize a cathode ray tube having a plurality of electron beam guns supported in the ray tube neck which are directed toward a multicolor producing viewing screen on the interior of the cathode ray tube faceplate. Horizontal and vertical scan systems are operative upon the electron beams produced by the plural electron guns to deflect the electron beams horizontally and vertical in a raster scanning pattern to sequentially scan the phosphor screen. A shadow mask or similar masking device is interposed between the electron beam guns and the phosphor screen to cause each electron beam to fall exclusively upon a particular set of color phosphor screen areas. The electron beams are intensity modulated in synchronism with the scanning process to produce the displayed image. Color is achieved by varying the ratios or relative electron beam intensities while brightness variations are obtained by varying the plural electron beams as a group.
In many television receivers, the black and white or luminance information is separately processed and amplified prior to its combination with the color difference signals to produce color video signals which are used to intensity modulate the individual electron beams within the cathode ray tube display. Because black and dark grey image areas are produced by low currents and light greys and whites are produced by high beam currents, the display of very light grey or white image portions (so-called "peak white") necessitates correspondingly high cathode ray tube electron beam currents. As a result, high amplitude peak white image portions often cause the display system to produce cathode ray tube beam currents which exceed the focusing capability of the display. As a result, a phenomenon known as "blooming" occurs which is characterized by the production of bright areas which are undesirably enlarged and appear poorly defined or blurred.
To address this problem practitioners in the art have employed systems such as brightness limiters responsive to average beam current to control or limit average cathode ray tube beam current. Other approaches have included high voltage responsive gain controls as well as complex signal gain feedback systems operative within the luminance channel.
While the foregoing described prior art systems have to some extent been effective, they often tend to be overly complex and expensive and have, in some instances, been found to degrade display performance. There remains, therefore, a continuing need in the art for a simple, effective and low cost system for controlling and compensating peak white signal conditions within television receiver cathode ray tube displays.
Accordingly, it is a general object of the present invention to provide an improved video processing system for television receivers. It is a more particular object to provide an improved video signal processing system for television receivers which is inexpensive, simple, and effective in the control of peak white display system response.